Trichlorosilane is frequently used as raw gas for preparing polysilicon which is a raw material of wafers of semiconductors for electronic products and solar cells. Further, the trichlorosilane is a chemical material having high commercial utilization such as being used even in preparation of fine chemical gases or compounds containing a silicon element such as monosilane (MS; SiH4).
In order to prepare the trichlorosilane, in a fluidized bed reactor, a mixing type reactor, or a fixed bed reactor, a method for reacting metal grade silicon (MG-Si) having purity of approximately 98 to 99% and hydrogen chloride (HCl) has been frequently used. However, in the case of using the method, there are problems in that a large amount of silicon tetrachloride is generated as byproducts and even in a precipitation process of preparing polysilicon using the trichlorosilane, a large amount of silicon tetrachloride is generated as byproducts.
In order to solve the problems, the silicon tetrachloride generated as the byproducts is converted into the trichlorosilane, and thus, reused, and eventually, research and development for improving the yield of the trichlorosilane have been actively conducted.
In order to convert the silicon tetrachloride into the trichlorosilane, generally, a process of hydrogen addition reaction (STC hydrogenation: SiCl4+H2→SiHCl3+HCl) in which the trichlorosilane is obtained by adding hydrogen to the silicon tetrachloride and then reacting them under a normal pressure condition and a temperature condition of 800 to 950° C. has been used. Recently, a process of STC hydrochlorination (MG-Si+3SiCl4+2H2→4SiHCl3) which is performed under the pressure condition of tens bars or more and the temperature condition of 500 to 700° C. has been frequently used. In the STC hydrochlorination process, exceptively, in some cases, a transition metal such as copper may be added as a catalyst. However, in the conversion process of the silicon tetrachloride, there are problems in that a reaction condition is difficult, power consumption is large, and undesired chlorosilane gas is generated to reduce the yield of the trichlorosilane. Further, there is a problem in that the silicon tetrachloride is in contact with air or water to generate silicon oxide and hydrogen chloride gas and thus wastes that cause environmental pollution are mass-produced. Further, in the process of converting the silicon tetrachloride into the trichlorosilane, the trichlorosilane as the product may be contaminated by a catalyst component and a metal impurity contained in the metal grade silicon, and as a result, there is a problem in that an additional purifying process is required and the trichlorosilane may not be obtained with high yield.
In order to solve the problems, various processing techniques for preparing the trichlorosilane from the silicon tetrachloride have been proposed.
For example, in U.S. Pat. No. 7,754,175 (Prior Art 1) or U.S. Pat. No. 7,056,484 (Prior Art 2), techniques of reacting metal grade silicon and hydrogen chloride (HCl) or reacting metal grade silicon with silicon tetrachloride, hydrogen, and hydrogen chloride are disclosed. In Prior Art 2, it is mentioned that it is important to reduce a particle size to a predetermined level or less by simultaneously grinding the metal grade silicon and the copper catalyst.
Further, in U.S. Pat. No. 8,197,784 (Prior Art 3), a technique of reacting silicon tetrachloride and hydrogen under a condition of 900 to 1,300° C. and 19 to 24 atm to obtain the trichlorosilane with high yield is disclosed. In Prior Art 3, it is disclosed that it is important that a ratio of silicon tetrachloride and hydrogen is adjusted in the range of 1:1 to 1:100.
Further, in US Patent Publication No. 2004/0022713 (Prior Art 4), a technique of reacting metal grade silicon with hydrogen and silicon tetrachloride in the presence of a catalyst or selectively adding thereto and reacting them with hydrogen chloride (HCl) is disclosed. In Prior Art 4, it is mentioned that it is important to maintain the size of the catalyst (copper oxide, copper halogenide, iron powder, iron halogenide) at the level of 1/30 to 1/100 as compared with the size of the metal grade silicon.
Further, in U.S. Pat. No. 7,462,341 (Prior Art 5), a technique of reacting metal grade silicon containing chrome with hydrogen chloride (HCl) under the conditions of 250 to 1,100° C. and 5 to 30 atm is disclosed. In Prior Art 5, particularly, it is disclosed that it is important that chrome is included in the metal grade silicon at a concentration of 30 to 10,000 ppm.
Further, in U.S. Pat. No. 5,871,705 (Prior Art 6), a technique of introducing at least one silane selected from dichlorosilane (DCS; SiH2C2), monochlorosilane (MCS; SiH3Cl), and monosilane to a reaction process of metal grade silicon and hydrogen chloride (HCl) is disclosed. In Prior Art 6, it is disclosed that it is important that an alkali metal compound is present together in the reaction of the metal grade silicon and the hydrogen chloride (HCl).
Meanwhile, in Japanese Patent Publication No. 1981-073617 (Prior Art 6), a technique of using copper power as a catalyst and reacting metal grade silicon, silicon tetrachloride, and hydrogen together at a reaction temperature of 350 to 600° C. to prepare trichlorosilane is disclosed. Further, in Japanese Patent Publication No. 1983-011042 (Prior Art 7), a technique of using copper chloride (CuCl) instead of copper power as a catalyst and reacting metal grade silicon, silicon tetrachloride, and hydrogen together to prepare trichlorosilane is disclosed. However, in the process of preparing the trichlorosilane, the catalyst such as copper (Cu) powder or copper chloride (CuCl) reduces the yield of the trichlorosilane due to a property of aggregation between the catalysts.
Further, in Japanese Patent Publication No. 1998-029813 (Prior Art 8), in order to solve a phenomenon in which catalysts such as copper (Cu) powder or copper chloride (CuCl) are aggregated with each other and enhance the yield of the trichlorosilane, a technique of using a copper silicide catalyst during STC hydrochlorination is disclosed. However, in Prior Art 8, there is a problem in that a silicon component included in the catalysts as well as the metal grade silicon participates in the trichlorosilane generating reaction. In addition, in the reaction process disclosed in Prior Art 8, while the catalyst supplied together with the metal grade silicon is fluidized, since the catalyst is discharged from the reactor in a chloride form together with the reaction product, there is a problem in that the catalyst needs to be continuously supplied and process operating cost for removing the catalyst from the reaction product after reaction is additionally generated. Further, even though the catalyst remains in the reactor, there is a problem in that in order to maintain a proper catalyst amount, the catalyst needs to be continuously supplied.